GDB remote protocol supports reverse debugging of the targets.
It includes 'reverse step' and 'reverse continue' operations.
The first one finds the previous step of the execution,
and the second one is intended to stop at the last breakpoint that
would happen when the program is executed normally.

Reverse debugging is possible in the replay mode, when at least
one snapshot was created at the record or replay phase.
QEMU can use these snapshots for travelling back in time with GDB.

Running the execution in replay mode allows using GDB reverse debugging
commands:
 - reverse-stepi (or rsi): Steps one instruction to the past.
   QEMU loads on of the prior snapshots and proceeds to the desired
   instruction forward. When that step is reaches, execution stops.
 - reverse-continue (or rc): Runs execution "backwards".
   QEMU tries to find breakpoint or watchpoint by loaded prior snapshot
   and replaying the execution. Then QEMU loads snapshots again and
   replays to the latest breakpoint. When there are no breakpoints in
   the examined section of the execution, QEMU finds one more snapshot
   and tries again. After the first snapshot is processed, execution
   stops at this snapshot.

The set of patches include the following modifications:
 - gdbstub update for reverse debugging support
 - functions that automatically perform reverse step and reverse
   continue operations
 - hmp/qmp commands for manipulating the replay process
 - improvement of the snapshotting for saving the execution step
   in the snapshot parameters
 - other record/replay fixes

The patches are available in the repository:
https://github.com/ispras/qemu/tree/rr-190419

v16 changes:
 - rebased to 4.0

v15 changes:
 - rebased to the new master
 - removed obsolete rtc patch
 - fixed misprint in the test

v14 changes:
 - rebased to the new master

v13 changes:
 - rebased to make QAPI stuff applicable
 - minor reverse step/reverse continue fix

v12 changes:
 - style fixes

v11 changes:
 - added can_do_io resetting before jumping to the next block in the chain
 - rebase to the latest master

v10 changes:
 - added patch for correct deadline calculation with external timers
 - updated icount-related documentation in json files
   (suggested by Markus Armbruster)
 - fixed replay shutdown
 - renamed some functions and variables to make them consistent with
   the documentation and displayed messages
 - minor changes

v9 changes:
 - moved rr qapi stuff to the separate file (suggested by Markus Armbruster)
 - minor coding style fixes

v8 changes:
 - rebased to the new master
 - added missing fix for prior rr patch
 - updated 'since' version number in json-related patches

v7 changes:
 - rebased to the new master with upstreamed patches from the series
 - several improvements in hmp/qmp commands handling (suggested by Markus Armbruster)
 - fixed record/replay with '-rtc base' option enabled
 - added document with virtual hardware requirements

v6 changes:
 - rebased to the new version of master
 - fixed build of linux-user configurations
 - added new clock for slirp and vnc timers

v5 changes:
 - multiple fixes of record/replay bugs appeared after QEMU core update
 - changed reverse debugging to 'since 3.1'

v4 changes:
 - changed 'since 2.13' to 'since 3.0' in json (as suggested by Eric Blake)

v3 changes:
 - Fixed PS/2 bug with save/load vm, which caused failures of the replay.
 - Rebased to the new code base.
 - Minor fixes.

v2 changes:
 - documented reverse debugging
 - fixed start vmstate loading in record mode
 - documented qcow2 changes (as suggested by Eric Blake)
 - made icount SnapshotInfo field optional (as suggested by Eric Blake)
 - renamed qmp commands (as suggested by Eric Blake)
 - minor changes

---

Pavel Dovgalyuk (23):
      block: implement bdrv_snapshot_goto for blkreplay
      replay: disable default snapshot for record/replay
      replay: update docs for record/replay with block devices
      replay: don't drain/flush bdrv queue while RR is working
      replay: finish record/replay before closing the disks
      qcow2: introduce icount field for snapshots
      migration: introduce icount field for snapshots
      replay: provide an accessor for rr filename
      qapi: introduce replay.json for record/replay-related stuff
      replay: introduce info hmp/qmp command
      replay: introduce breakpoint at the specified step
      replay: implement replay-seek command
      replay: refine replay-time module
      replay: flush rr queue before loading the vmstate
      gdbstub: add reverse step support in replay mode
      gdbstub: add reverse continue support in replay mode
      replay: describe reverse debugging in docs/replay.txt
      replay: add BH oneshot event for block layer
      replay: document development rules
      util/qemu-timer: refactor deadline calculation for external timers
      replay: fix replay shutdown
      replay: rename step-related variables and functions
      icount: clean up cpu_can_io before jumping to the next block

pbonzini@redhat.com (1):
      replay: add missing fix for internal function


 MAINTAINERS               |    1 
 accel/tcg/tcg-runtime.c   |    2 
 accel/tcg/translator.c    |    1 
 block/blkreplay.c         |    8 +
 block/block-backend.c     |    8 +
 block/io.c                |   32 ++++
 block/iscsi.c             |    5 -
 block/nfs.c               |    5 -
 block/null.c              |    4 -
 block/nvme.c              |    6 +
 block/qapi.c              |   18 ++
 block/qcow2-snapshot.c    |    9 +
 block/qcow2.h             |    2 
 block/rbd.c               |    5 -
 block/vxhs.c              |    5 -
 blockdev.c                |   10 +
 cpus.c                    |   30 +++-
 docs/devel/replay.txt     |   46 ++++++
 docs/interop/qcow2.txt    |    4 +
 docs/replay.txt           |   45 ++++++
 exec.c                    |    8 +
 gdbstub.c                 |   52 +++++++
 hmp-commands-info.hx      |   14 ++
 hmp-commands.hx           |   53 +++++++
 hmp.h                     |    4 +
 include/block/snapshot.h  |    1 
 include/qemu/timer.h      |    7 -
 include/sysemu/replay.h   |   30 ++++
 migration/savevm.c        |   11 ++
 qapi/Makefile.objs        |    2 
 qapi/block-core.json      |    8 +
 qapi/block.json           |    3 
 qapi/misc.json            |   18 --
 qapi/qapi-schema.json     |    1 
 qapi/replay.json          |  121 +++++++++++++++++
 qtest.c                   |    2 
 replay/Makefile.objs      |    3 
 replay/replay-debugging.c |  327 +++++++++++++++++++++++++++++++++++++++++++++
 replay/replay-events.c    |   18 ++
 replay/replay-internal.c  |   10 +
 replay/replay-internal.h  |   17 +-
 replay/replay-snapshot.c  |    6 -
 replay/replay-time.c      |   36 ++---
 replay/replay.c           |   56 ++++++--
 stubs/Makefile.objs       |    1 
 stubs/replay-user.c       |    9 +
 stubs/replay.c            |   10 +
 tests/ptimer-test-stubs.c |    4 -
 tests/ptimer-test.c       |    4 -
 util/qemu-timer.c         |   41 +++++-
 vl.c                      |   11 +-
 51 files changed, 1003 insertions(+), 131 deletions(-)
 create mode 100644 docs/devel/replay.txt
 create mode 100644 qapi/replay.json
 create mode 100644 replay/replay-debugging.c
 create mode 100644 stubs/replay-user.c

-- 
Pavel Dovgalyuk

Ping.
Can anyone PULL these patches?

Pavel Dovgalyuk

> -----Original Message-----
> From: Pavel Dovgalyuk [mailto:pavel.dovgaluk@gmail.com]
> Sent: Monday, April 22, 2019 2:20 PM
> To: qemu-devel@nongnu.org
> Cc: kwolf@redhat.com; peter.maydell@linaro.org; war2jordan@live.com;
> crosthwaite.peter@gmail.com; boost.lists@gmail.com; artem.k.pisarenko@gmail.com;
> quintela@redhat.com; ciro.santilli@gmail.com; jasowang@redhat.com; mst@redhat.com;
> armbru@redhat.com; mreitz@redhat.com; maria.klimushenkova@ispras.ru; dovgaluk@ispras.ru;
> kraxel@redhat.com; pavel.dovgaluk@ispras.ru; thomas.dullien@googlemail.com;
> pbonzini@redhat.com; alex.bennee@linaro.org; dgilbert@redhat.com; rth@twiddle.net
> Subject: [PATCH for-4.1 00/24] Fix record/replay and add reverse debugging
> 
> GDB remote protocol supports reverse debugging of the targets.
> It includes 'reverse step' and 'reverse continue' operations.
> The first one finds the previous step of the execution,
> and the second one is intended to stop at the last breakpoint that
> would happen when the program is executed normally.
> 
> Reverse debugging is possible in the replay mode, when at least
> one snapshot was created at the record or replay phase.
> QEMU can use these snapshots for travelling back in time with GDB.
> 
> Running the execution in replay mode allows using GDB reverse debugging
> commands:
>  - reverse-stepi (or rsi): Steps one instruction to the past.
>    QEMU loads on of the prior snapshots and proceeds to the desired
>    instruction forward. When that step is reaches, execution stops.
>  - reverse-continue (or rc): Runs execution "backwards".
>    QEMU tries to find breakpoint or watchpoint by loaded prior snapshot
>    and replaying the execution. Then QEMU loads snapshots again and
>    replays to the latest breakpoint. When there are no breakpoints in
>    the examined section of the execution, QEMU finds one more snapshot
>    and tries again. After the first snapshot is processed, execution
>    stops at this snapshot.
> 
> The set of patches include the following modifications:
>  - gdbstub update for reverse debugging support
>  - functions that automatically perform reverse step and reverse
>    continue operations
>  - hmp/qmp commands for manipulating the replay process
>  - improvement of the snapshotting for saving the execution step
>    in the snapshot parameters
>  - other record/replay fixes
> 
> The patches are available in the repository:
> https://github.com/ispras/qemu/tree/rr-190419
> 
> v16 changes:
>  - rebased to 4.0
> 
> v15 changes:
>  - rebased to the new master
>  - removed obsolete rtc patch
>  - fixed misprint in the test
> 
> v14 changes:
>  - rebased to the new master
> 
> v13 changes:
>  - rebased to make QAPI stuff applicable
>  - minor reverse step/reverse continue fix
> 
> v12 changes:
>  - style fixes
> 
> v11 changes:
>  - added can_do_io resetting before jumping to the next block in the chain
>  - rebase to the latest master
> 
> v10 changes:
>  - added patch for correct deadline calculation with external timers
>  - updated icount-related documentation in json files
>    (suggested by Markus Armbruster)
>  - fixed replay shutdown
>  - renamed some functions and variables to make them consistent with
>    the documentation and displayed messages
>  - minor changes
> 
> v9 changes:
>  - moved rr qapi stuff to the separate file (suggested by Markus Armbruster)
>  - minor coding style fixes
> 
> v8 changes:
>  - rebased to the new master
>  - added missing fix for prior rr patch
>  - updated 'since' version number in json-related patches
> 
> v7 changes:
>  - rebased to the new master with upstreamed patches from the series
>  - several improvements in hmp/qmp commands handling (suggested by Markus Armbruster)
>  - fixed record/replay with '-rtc base' option enabled
>  - added document with virtual hardware requirements
> 
> v6 changes:
>  - rebased to the new version of master
>  - fixed build of linux-user configurations
>  - added new clock for slirp and vnc timers
> 
> v5 changes:
>  - multiple fixes of record/replay bugs appeared after QEMU core update
>  - changed reverse debugging to 'since 3.1'
> 
> v4 changes:
>  - changed 'since 2.13' to 'since 3.0' in json (as suggested by Eric Blake)
> 
> v3 changes:
>  - Fixed PS/2 bug with save/load vm, which caused failures of the replay.
>  - Rebased to the new code base.
>  - Minor fixes.
> 
> v2 changes:
>  - documented reverse debugging
>  - fixed start vmstate loading in record mode
>  - documented qcow2 changes (as suggested by Eric Blake)
>  - made icount SnapshotInfo field optional (as suggested by Eric Blake)
>  - renamed qmp commands (as suggested by Eric Blake)
>  - minor changes
> 
> ---
> 
> Pavel Dovgalyuk (23):
>       block: implement bdrv_snapshot_goto for blkreplay
>       replay: disable default snapshot for record/replay
>       replay: update docs for record/replay with block devices
>       replay: don't drain/flush bdrv queue while RR is working
>       replay: finish record/replay before closing the disks
>       qcow2: introduce icount field for snapshots
>       migration: introduce icount field for snapshots
>       replay: provide an accessor for rr filename
>       qapi: introduce replay.json for record/replay-related stuff
>       replay: introduce info hmp/qmp command
>       replay: introduce breakpoint at the specified step
>       replay: implement replay-seek command
>       replay: refine replay-time module
>       replay: flush rr queue before loading the vmstate
>       gdbstub: add reverse step support in replay mode
>       gdbstub: add reverse continue support in replay mode
>       replay: describe reverse debugging in docs/replay.txt
>       replay: add BH oneshot event for block layer
>       replay: document development rules
>       util/qemu-timer: refactor deadline calculation for external timers
>       replay: fix replay shutdown
>       replay: rename step-related variables and functions
>       icount: clean up cpu_can_io before jumping to the next block
> 
> pbonzini@redhat.com (1):
>       replay: add missing fix for internal function
> 
> 
>  MAINTAINERS               |    1
>  accel/tcg/tcg-runtime.c   |    2
>  accel/tcg/translator.c    |    1
>  block/blkreplay.c         |    8 +
>  block/block-backend.c     |    8 +
>  block/io.c                |   32 ++++
>  block/iscsi.c             |    5 -
>  block/nfs.c               |    5 -
>  block/null.c              |    4 -
>  block/nvme.c              |    6 +
>  block/qapi.c              |   18 ++
>  block/qcow2-snapshot.c    |    9 +
>  block/qcow2.h             |    2
>  block/rbd.c               |    5 -
>  block/vxhs.c              |    5 -
>  blockdev.c                |   10 +
>  cpus.c                    |   30 +++-
>  docs/devel/replay.txt     |   46 ++++++
>  docs/interop/qcow2.txt    |    4 +
>  docs/replay.txt           |   45 ++++++
>  exec.c                    |    8 +
>  gdbstub.c                 |   52 +++++++
>  hmp-commands-info.hx      |   14 ++
>  hmp-commands.hx           |   53 +++++++
>  hmp.h                     |    4 +
>  include/block/snapshot.h  |    1
>  include/qemu/timer.h      |    7 -
>  include/sysemu/replay.h   |   30 ++++
>  migration/savevm.c        |   11 ++
>  qapi/Makefile.objs        |    2
>  qapi/block-core.json      |    8 +
>  qapi/block.json           |    3
>  qapi/misc.json            |   18 --
>  qapi/qapi-schema.json     |    1
>  qapi/replay.json          |  121 +++++++++++++++++
>  qtest.c                   |    2
>  replay/Makefile.objs      |    3
>  replay/replay-debugging.c |  327 +++++++++++++++++++++++++++++++++++++++++++++
>  replay/replay-events.c    |   18 ++
>  replay/replay-internal.c  |   10 +
>  replay/replay-internal.h  |   17 +-
>  replay/replay-snapshot.c  |    6 -
>  replay/replay-time.c      |   36 ++---
>  replay/replay.c           |   56 ++++++--
>  stubs/Makefile.objs       |    1
>  stubs/replay-user.c       |    9 +
>  stubs/replay.c            |   10 +
>  tests/ptimer-test-stubs.c |    4 -
>  tests/ptimer-test.c       |    4 -
>  util/qemu-timer.c         |   41 +++++-
>  vl.c                      |   11 +-
>  51 files changed, 1003 insertions(+), 131 deletions(-)
>  create mode 100644 docs/devel/replay.txt
>  create mode 100644 qapi/replay.json
>  create mode 100644 replay/replay-debugging.c
>  create mode 100644 stubs/replay-user.c
> 
> --
> Pavel Dovgalyuk

"Pavel Dovgalyuk" <dovgaluk@ispras.ru> writes:

> Ping.
> Can anyone PULL these patches?

Paolo?

> From: Markus Armbruster [mailto:armbru@redhat.com]
> "Pavel Dovgalyuk" <dovgaluk@ispras.ru> writes:
> 
> > Ping.
> > Can anyone PULL these patches?
> 
> Paolo?

Is there anything new?

Pavel Dovgalyuk